Does our Miata need individual throttle bodies? | Garage Rescue Miata

Pete. (l33t FS) said:

mke said:

I'll add this, unlike with carbs there is very little downside to a TB that is bigger than needed.  The bigger the TB the harder is it to get a smooth off idle transition and it theory it could cost HP because there is more air mass in the intake track to accelerate so velocity should in theory decreases.  In practice though the stuff I've tried or seen tried what happens is the hp goes up as TB size goes up until a bigger TB no longer helps....I've never seen the hp start coming back down, not to say it couldn't, but I've not seen it. 

  That is still an eight valve head.  He described the intake as having "only" 55mm throttle bodies. 

That is, 55mm per cylinder.

I'm not familar with that application but  mine are 54mm because they were the biggest I could get for relatively little money ($50 each) and are costing about 0.5-1% on the flow bench so 55 or 56 would have been my preference if available. There is a company doing a 58mm conversion on them I saw...for another 300 each!  so that is not happening   I did cut the side of the shafts flat which added about 2% or so iirc to get me to were I am.

Mine are off a ducati 749/999 (well 6 actually) so 375-500cc per TB from the factory and I'm at about 450cc and that sizing seems about spot on with big valves and a high flowing port....its really hp/cyl whic is really flow/cyl that you're trying to match, no idea how that translates to a roary though?  Anyway,  the stock 308 or TR head flow about 60% of what I have now and on those 44mm from a zx14 or hayabusa seemed about right and I helped a couple guys install them on their 308s, one a 4V, one a 2V, both heads flow exactly the same stock btw, the 4v just needs less cam for the same hp numbers so better for pollution regs I guess.  Anyway, these are 3 liter V8s making a little south of 300hp so pretty much the same as a 1.6 or 1.8liter 4 making up to about 150hp and 150hp is right about what those bikes made stock so again everything kind of matches up to the expectation.  A smaller but higher output engine is generally more sensitive to small flow changes so something that works well on a big V8 making 50hp/cylinder is probably too small on a little 4 banger making the same 50hp/cyl. So were it me, I'd be looking for an option right around 44mm for an application like this (miata) I think.

Last thought is a TB flows better and a carb of the same size...a TB is an empty tube, a carb has stuff mucking up the air flow so when you see people switch from carbs to efi and pick up hp its usually that they had carbs that were too small and replaced with the same size TB, which is effectively bigger so they added the flow they needed, at least this is true for race engine.  On street engines you really don't have a choice but to run the carbs a bit smaller than optimal hp wise as that is the only way to keep the bottom and midrange working well and that is were street engine live 99% of the time so you just have to get that working right.  With EFI and TBs, that is basically a non-issue so I err on the large size if unsure and use a nice progressive throttle pedal linkage to give good throttle position control at small openings where a small change in throttle position makes a big airflow change so its easy to drive around town. 

With DBW so common getting a progression you like just means changing numbers in a table, not not reworking linkages.  This is how the table I use on the frankenferrari...you see the lower left the pedal move a lot for small changes in the TBs then on the upper right the TBs are moving much quick where there is a much smaller % flow change from a % position change.  at idle with the pedal full up the TBs are at 6%...this was high idle on a not well running engine so real idle will probably be say 4% but 6 for now....then when the pedal is at 20% the tbs are at 10%, so only a 4% change and that seemed about right playing with it in the garage...very progressive because that small position change will more than double air flow into the engine.  As I said in my 1st post, its the small things like this that can be really frustrating about ITB setups when you get them wrong.  ITBs are wonderful when they are right, but getting them right, especially on a street car, often takes a bit of patience.

You guys want a great deal on my Wossner 12:1 1.6 pistons and REALLY make it scream? These came with an engine I bought and I'm probably never going to use them...

In reply to accordionfolder :

Please show yourself out. I mean, What more can you tell us about them? 

12:1, cams,  E85 and ITBs would make for a properly spicy fun setup. 

In reply to mke :

Ever look under the hood of a 2.3l OHC powered Ford?  That, on steroids.

Esslinger made quite a name for themselves building fast Lima based engines.  I say "based" because they make their own heads and blocks, including tall deck blocks for the 3l+ engines.  Bring a styrofoam cooler full of money. 

Not all that different from what guys who rally Volvos do with redblock engines where class rules limit them to stock engine architecture and number of valves.

David S. Wallens said:

In reply to accordionfolder :

Please show yourself out. I mean, What more can you tell us about them? 

Lol, not much to say! I was hoping for 150obo + shipping. They're 500 new, and these are bnib. I think they'd make a super neat build especially with the availability of e85, just not enough time!

**Edit, apparently 650 new.

https://www.vividracing.com/wossner-16l-785mm-121-pistons-mazda-miata-19901993-p-132253.html

"while you're in there...."

In reply to Keith Tanner :

2 years and $30,000 later, the car is so upgraded that it is sold at a huge loss and a bone stock NA is purchased because it's more pleasant to drive, look forward to spending time behind the wheel instead of dreading it.

Pete. (l33t FS) said:

In reply to Keith Tanner :

2 years and $30,000 later, the car is so upgraded that it is sold at a huge loss and a bone stock NA is purchased because it's more pleasant to drive, look forward to spending time behind the wheel instead of dreading it.

Every project.

Pete. (l33t FS) said:

In reply to Keith Tanner :

2 years and $30,000 later, the car is so upgraded that it is sold at a huge loss and a bone stock NA is purchased because it's more pleasant to drive, look forward to spending time behind the wheel instead of dreading it.

Stock 1.6 cars are fantastic for the road, but on track or autoX ... Man they're incredibly slow. Good character, but literally ~6 seconds a lap to a stock VVT engine at NCM, same tires and setup. I drove one for a whole season in 2020 and loved it, but even 141 whp from my VVT car might as well be a rocket ship compared to it.

In reply to accordionfolder :

I can vouch for this.  Compared to a worn out 1.6, a stock VVT 1.8 at ~140hp is a LOT of fun.  But it's still not really fast... 

DeadSkunk (Warren) said:

Wanna screw with people? Put four SU carbs on it with the pistons locked up in place so that they're just throttle bodies.........

SU sort of did that themselves (I owned a pair of these).

One thing I do like about the Miata's current setup: It uses pump fuel and, as a result, I can fuel up anywhere. It doesn't have a huge tank, and on the highway the engine turns about 4500 rpm. Being able to fill up anywhere has been nice. (I know, think about the editorial....)

In reply to wspohn :

the 2 barrels are cool , how rare are they and what did they come on ?

Thanks

californiamilleghia said:

In reply to wspohn :

the 2 barrels are cool , how rare are they and what did they come on ?

Thanks

The DU6 carbs were very rare back in the day. They used them on the Lotus FPF engines (used in F1 cars), Cooper Monacos, briefly experimentally in MGA Twin Cam factory racers, and the Triumph TRS Le Mans cars.

Very, very rare for many years, they are now being reproduced for Jaguars etc. at pretty eye-watering prices.  I played around with them a bit as I was setting up an MGA Twin Cam for racing, but I decided (wisely, I think) to go with the more easily tunable 45 DCOE Webers, just as the factory had done.  

Should have hung them on the wall as garage trophies but sold them to someone who was restoring one of the TRS cars.

ITBs and bear wheels so that the induction noise from the ITBs can be referenced as the growl of the bear. Or you can go panda with it and turn a bamboo shift knob. There is 3D printing filament that is made from bamboo as well for some questionable theme ideas. Such as a bamboo printed pi dash surround, bamboo spoiler risers, etc. 

By the way, still thinking about this. :) 

Having went from a 4cyl twin carb setup to ITBs. On a 1.8 boxer.         

It seems the throttle bodies, manifold, fuel rail, and linkage (for precise throttle movement) is less than half the work.

The stand alone ECU installation and going beyond a base tune is the rest. It was worth it in my case: Learning curve and all was an upgrade.  Went to bigger injectors for my 42mm throttle bodies.

My Z4M (S54 engine) has ITBs and I had noticed some of the owners of the Z4 3.0 (M54 engine) tried fitting the ITBs to their engines.  Without any other changes, the difference in output was miniscule but their expense would have gone a long way toward buying a turbo for the car.

I'd forgotten about this thread, but when it popped up again I went back and watched Keith's whole video over again - very enjoyable!

In reply to wspohn :

The beauty is not the peak power, though. The beauty is that there is atmospheric pressure 5 inches from the valves at all times so when you open the throttle the response is RIGHT THERE.  With a plenum manifold you can make more power (no throttle shafts in the inlet ports) but response is soggy because when you whack the throttle there is a liter or two of volume that needs to come up to atmospheric before the valves see the increase in pressure.  And at part throttle with big cams, reversion at intake closing pushes air into the plenum, which means the intake port is moving backwards, takes effort to get it moving forwards again. 

And with high valve overlap, the way the vacuum in the port dies quickly at part throttle with ITBs means less exhaust reversion into the intake = better idle and low speed drivability.

Pros and cons.  Want peak power? Plenum manifold.  Want good response and low load drivability with antisocially large camshafts? ITB.

That last comment needs moar canoe!

DWNSHFT said:

That last comment needs moar canoe!

What comment? 

Pete. (l33t FS) said:

Pros and cons.  Want peak power? Plenum manifold.  Want good response and low load drivability with antisocially large camshafts? ITB.

Stop it.  I've successfully avoided completing installation of Yamaha R1 ITBs on my cammed-up 7A-GE for a long time now, and really do not need anyone watering that seed right now.

DarkMonohue said:

Pete. (l33t FS) said:

Pros and cons.  Want peak power? Plenum manifold.  Want good response and low load drivability with antisocially large camshafts? ITB.

Stop it.  I've successfully avoided completing installation of Yamaha R1 ITBs on my cammed-up 7A-GE for a long time now, and really do not need anyone watering that seed right now.

How big are the cams?

The ITB-ified bridge ported 13B in my "fun" car has low load/part throttle drivability like a stock engine.  Way way better than similar engines I have had using OE type manifolds or godawful plenum manifolds that I thought were a good idea at the time.

Pete. (l33t FS) said:

How big are the cams?

The ITB-ified bridge ported 13B in my "fun" car has low load/part throttle drivability like a stock engine.  Way way better than similar engines I have had using OE type manifolds or godawful plenum manifolds that I thought were a good idea at the time.

Not enormous. They're 226° @ .050" (Web 577).  Peak power comes in around 7000 RPM, though I am starting to wonder if it's not valvespring limited.   Drivability with a stock plenum style manifold is acceptable, but not inspiring.  Would be better with more time tuning the MS.